This invention relates to the coloring of color coded optical waveguides with a relatively thin coating of ultraviolet curable ink, and to other UV curing processes.
The use of optical fiber waveguides, either as individual fibers or as an array of a plurality of such fibers in a ribbon form for transmitting data has become the preferred mode of signal transmission. Optical fibers have extremely high information carrying capacity as compared to metal electrical conductors.
Optical fibers are both very small in diameter and are extremely fragile, thus making individual fibers hard to handle and manipulate. Thus, it has been the practice to combine large numbers of fibers in a cable, or in a fiber ribbon which comprises multiple fibers extending parallel to each other and encased in a matrix material. The large numbers of virtually identical fibers present in such combinations makes fiber connection and splicing almost impossible without some method of fiber identification. One such method that is widely used is color coding the individual fibers preferably in accordance with a standard code, such as is used for metal conductors. Such color coding, while efficacious, is difficult to achieve, especially in a production milieu where speed or high productive capacity is most desirable.
For example, it has not proven satisfactory to use conventional solvent based colorants, such as dyes, marking fluids, inks and the like for high speed color coding of optical glass fiber waveguides, since such solvent based colorant films are formed by evaporative drying of the solvent which is a relatively slow process. Also, solvent-based ink systems do not have the desired long term resistance to the solvents, oils, and gels encountered in the cable installation environment. Solvent-based colorants are also easily worn away by the physical abrasion typically encountered in cabling. Furthermore, such materials often contain environmentally undesirable solvents and are difficult to apply with sufficient precision to leave a truly uniform coating about the circumference of the optical fiber. As far as the application of liquid solvent inks is concerned, conventional ink application apparatus and techniques are not optimally suited for processing the optical fiber at high speeds of the order of 10 m/sec.
As stated above, optical glass fibers are very fragile and easily subject to damages. Typically, therefore, they are coated with one or several protective plastic coatings as are discussed in U.S. Pat. Nos. 4,125,644 and 4,344,669. These protective coatings are applied as soon as the fibers are formed to protect against abrasion during takeup and handling. It has been stated in U.S. Pat. No. 4,125,644 that various additives including pigments may be added to these protective plastic coatings, if desired. Thus, to some degree coloration of the exterior of the fiber by coloration of the protective coating may be accomplished by the fiber producer to assist him in identifying particular products. However, as noted in U.S. Pat. No. 4,125,644, the type and quantities of substances added to the buffer coatings must be selected with care to avoid disturbing the desired qualities of the coatings. Also, the addition of pigment additives to the buffer coatings can slow down the drawing and curing of the fibers and the overall fiber production speed. Furthermore, in the production of optical fiber cables, it is important that the physical and optical characteristics of the fiber waveguides in the cable be carefully matched, and it is often desirable that all of the fiber waveguides be from the same production run or lot. Thus, even though it may be known that colorants can be added to the buffer coatings, as noted above, it is not feasible for the fiber producer to attempt to color code the fibers for fiber identification purposes by this method.
It has been found that an optical fiber waveguide comprising a fiber having a protective coating thereon can be successfully color coded by providing it with an additional coating of a colored, ultraviolet (UV) cured ink applied as a very thin film of, for example, five to twelve (5 to 12) microns in thickness. Such a coating is applied and affixed by passing the fiber at a relative high speed through a coating apparatus and, subsequently, through a UV radiation curing apparatus or oven, and then winding the fiber on a take-up spool or passing it on to another production stage or stages where, ultimately, it is wound on a take-up spool.
Where the fibers are to be arrayed in a ribbon configuration, each optical fiber is enclosed in inner and outer layers of coating materials and is provided with a color identifier. The inner layer is comprised of a UV curable bonding material having a modulus in the range of about 1 M Pa. For mechanical protection, the outer layer is a UV curable bonding material having a modulus in the range of about 1 Gpa. When the optical fibers are disposed in the parallel array, interstices are created between the fibers and between the fiber and an envelope which is spaced about 25 xcexcm at its closest point to each fiber. A UV curable matrix bonding material which has a modulus having a value less than that of the outer coating layer on the fiber and more than that of the inner coating layer fills the interstices, extends to the peripheral line which defines the envelope, and bonds together the optical fibers. The modulus of the matrix material and the bond of the matrix material to the color identifier on the optical fibers is such that interfiber and interribbon movement is allowed. Also, accessing of the individual fibers is allowed upon the application of peeling forces by a craftsperson without the need for complex tools and without obfuscating the color identifier.
In both ribbon configurations and with individual fibers for cabling, for example, there is at least one UV ink curing step and, for ribbons, two UV curing steps. With the current family of inks, matrix materials, and the UV capabilities of the current coloring machines, coloring speeds are generally of the order of 10 meters/second to meet the prescribed cure levels. Ribbons made with fibers colored at higher coloring speeds cause detrimental changes in the operative properties of the ribbon. As a consequence, it has been the practice to limit the speed of the production process to assure a predetermined dose of UV radiation is applied to effect full cure of the ink colorant. Higher speeds can be realized if higher cure levels can be achieved such as by additional UV ovens or UV ovens of higher power; however, increasing the UV intensity or power also requires a major modification of equipment such as changing the entire oven, power supply and the exhaust system. Space limitations, as well as ergonomic and safety issues in existing coloring lines, make using additional UV ovens difficult, which would require significant changes in the xe2x80x9cfootprintxe2x80x9d of the coloring machine and complicate process control. Inasmuch as there is, presently, a huge investment in coloring machines and in the entire production coloring stage, remodeling the coloring stage to add one additional coloring machine would be an expensive proposition. New fiber production lines can allow for such additions, but current lines, in general, do not.
The present invention is a retrofit arrangement designed for use with existing color coding or ribboning UV curing apparatus for optical fiber waveguides to increase the speed of the fiber throughout the production process while maintaining a minimum dose of UV radiation, although it is not restricted to retrofitting existing equipment. As such, the apparatus of the invention does not require an increase in space or foot print of the curing apparatus, yet it results in greatly increased line speeds, hence increased fiber production per unit of time. Also, the invention provides improved uniformity of cure over the entire surface of the ink colorant because both sides of the fiber profile alternatively face the source of UV radiation. As pointed out hereinbefore, such higher line speeds have heretofore been achievable through the addition of one or more UV ovens which requires more space than present curing apparatus and renders the entire production line inoperative during the upgrade.
The present invention, in a first illustrative embodiment thereof, comprises a UV curing stage wherein the fiber, coated with ink of the desired color is passed through a UV curing oven at a considerably greater speed than heretofore used. At the line exit end of the oven are first and second turn-around sheaves which route the fiber, which is only partially cured, back to third and fourth sheaves which, in turn, route the fiber into and through the same UV oven for a second exposure to the UV radiation. The fiber emerging from the oven is then passed, by means of an exit or take-up sheave to other stages or to, ultimately, the fiber take-up and spooling apparatus. The path of the fiber in the second pass through the oven is off-set from the first path a distance sufficient to prevent touching of the fiber in the two paths, but less than the diameter of the xe2x80x9csweet spotxe2x80x9d of the UV radiation within the oven. When the apparatus is used in ribbon curing, this requires that the xe2x80x9csweet spotxe2x80x9d comprising the focused region of UV radiation be of a sufficient diameter to envelope completely both ribbon paths. With such an arrangement, the single UV oven assumes the functions of first and second ovens a comparable result, i.e., greater line speed, achievable heretofore only with an additional UV oven.
In a second preferred embodiment of the invention, the fiber emerging from the exit end of the UV oven is directed back into the oven through the exit end in the reverse direction by a single turn-around sheave, and passes therethrough in the opposite direction to the first path to second and third turn-around or idler sheaves which direct it to the take-up sheave and take-up mechanism. The second embodiment is somewhat simpler to set up than the first embodiment, but makes possible substantially the same end result, i.e., greater line speed.
In both embodiments of the invention, as well as variants thereof which may occur to workers in the art the residence time of the substrate in the presence of the UV curing radiation is approximately double that of exiting curing apparatus.
The numerous features and advantages of the present invention will be more fully apparent and understood from the following detailed description, read in conjunction with the accompanying drawings.